Method for obtaining operator network identification number of visited network

ABSTRACT

One disclosure of the present specification provides a method for a proxy-call session control function (P-CSCF) to obtain an identifier of a visited public land mobile network (V-PLMN) in order to register a user equipment (UE) roaming in the V-PLMN into an IP multimedia subsystem (IMS) network. The method may comprise the steps of: receiving a response message from an Interrogating-CSCF (I-CSCF) in response to the transmission of a REGISTER message for registering a user equipment into an IMS network; determining whether the received response message is a 401 unauthorized message; when the received response message is a 401 unauthorized message, transmitting the response message to the user equipment and generating an interface for transmitting and receiving data to and from an entity of an EPC network; and receiving an identifier of the V-PLMN from the entity of the EPC network.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the National Phase of PCT International ApplicationNo. PCT/KR2016/008873, filed on Aug. 12, 2016, which claims priorityunder 35 U.S.C. 119(e) to U.S. Provisional Application No. 62/209,886,filed on Aug. 26, 2015, all of which are hereby expressly incorporatedby reference into the present application.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to mobile communication.

Related Art

In 3GPP in which technical standards for mobile communication systemsare established, in order to handle 4th generation communication andseveral related forums and new technologies, research on Long TermEvolution/System Architecture Evolution (LTE/SAE) technology has startedas part of efforts to optimize and improve the performance of 3GPPtechnologies from the end of the year 2004

SAE that has been performed based on 3GPP SA WG2 is research regardingnetwork technology that aims to determine the structure of a network andto support mobility between heterogeneous networks in line with an LTEtask of a 3GPP TSG RAN and is one of recent important standardizationissues of 3GPP. SAE is a task for developing a 3GPP system into a systemthat supports various radio access technologies based on an IP, and thetask has been carried out for the purpose of an optimized packet-basedsystem which minimizes transmission delay with a more improved datatransmission capability.

An Evolved Packet System (EPS) higher level reference model defined in3GPP SA WG2 includes a non-roaming case and roaming cases having variousscenarios, and for details therefor, reference can be made to 3GPPstandard documents TS 23.401 and TS 23.402. A network configuration ofFIG. 1 has been briefly reconfigured from the EPS higher level referencemodel.

FIG. 1 shows the configuration of an evolved mobile communicationnetwork.

An Evolved Packet Core (EPC) may include various elements. FIG. 1illustrates a Serving Gateway (S-GW) 52, a Packet Data Network Gateway(PDN GW) 53, a Mobility Management Entity (MME) 51, a Serving GeneralPacket Radio Service (GPRS) Supporting Node (SGSN), and an enhancedPacket Data Gateway (ePDG) that correspond to some of the variouselements.

The S-GW 52 is an element that operates at a boundary point between aRadio Access Network (RAN) and a core network and has a function ofmaintaining a data path between an eNodeB 22 and the PDN GW 53.Furthermore, if a terminal (or User Equipment (UE) moves in a region inwhich service is provided by the eNodeB 22, the S-GW 52 plays a role ofa local mobility anchor point. That is, for mobility within an E-UTRAN(i.e., a Universal Mobile Telecommunications System (Evolved-UMTS)Terrestrial Radio Access Network defined after 3GPP release-8), packetscan be routed through the S-GW 52. Furthermore, the S-GW 52 may play arole of an anchor point for mobility with another 3GPP network (i.e., aRAN defined prior to 3GPP release-8, for example, a UTRAN or GlobalSystem for Mobile communication (GSM) (GERAN)/Enhanced Data rates forGlobal Evolution (EDGE) Radio Access Network).

The PDN GW (or P-GW) 53 corresponds to the termination point of a datainterface toward a packet data network. The PDN GW 53 can support policyenforcement features, packet filtering, charging support, etc.Furthermore, the PDN GW (or P-GW) 53 can play a role of an anchor pointfor mobility management with a 3GPP network and a non-3GPP network(e.g., an unreliable network, such as an Interworking Wireless LocalArea Network (I-WLAN), a Code Division Multiple Access (CDMA) network,or a reliable network, such as WiMax).

In the network configuration of FIG. 1, the S-GW 52 and the PDN GW 53have been illustrated as being separate gateways, but the two gatewaysmay be implemented in accordance with a single gateway configurationoption.

The MME 51 is an element for performing the access of a terminal to anetwork connection and signaling and control functions for supportingthe allocation, tracking, paging, roaming, handover, etc. of networkresources. The MME 51 controls control plane functions related tosubscribers and session management. The MME 51 manages numerous eNodeBs22 and performs conventional signaling for selecting a gateway forhandover to another 2G/3G networks. Furthermore, the MME 51 performsfunctions, such as security procedures, terminal-to-network sessionhandling, and idle terminal location management.

The SGSN handles all packet data, such as a user's mobility managementand authentication for different access 3GPP networks (e.g., a GPRSnetwork and an UTRAN/GERAN).

The ePDG plays a role of a security node for an unreliable non-3GPPnetwork (e.g., an I-WLAN and a Wi-Fi hotspot).

As described with reference to FIG. 1, a terminal (or UE) having an IPcapability can access an IP service network (e.g., IMS), provided by aservice provider (i.e., an operator), via various elements within an EPCbased on non-3GPP access as well as based on 3GPP access.

Furthermore, FIG. 1 shows various reference points (e.g., S1-U andS1-MME). In a 3GPP system, a conceptual link that connects two functionsthat are present in the different function entities of an E-UTRAN and anEPC is called a reference point. Table 1 below defines reference pointsshown in FIG. 1. In addition to the reference points shown in theexample of Table 1, various reference points may be present depending ona network configuration.

TABLE 1 REFERENCE POINT DESCRIPTION S1-MME A reference point for acontrol plane protocol between the E-UTRAN and the MME S1-U A referencepoint between the E-UTRAN and the S-GW for path switching betweeneNodeBs during handover and user plane tunneling per bearer S3 Areference point between the MME and the SGSN that provides the exchangeof pieces of user and bearer information for mobility between 3GPPaccess networks in idle and/or activation state. This reference pointcan be used intra-PLMN or inter-PLMN (e.g. in the case of Inter-PLMNHO). S4 A reference point between the SGW and the SGSN that providesrelated control and mobility support between the 3GPP anchor functionsof a GPRS core and the S-GW. Furthermore, if a direct tunnel is notestablished, the reference point provides user plane tunneling. S5 Areference point that provides user plane tunneling and tunnel managementbetween the S- GW and the PDN GW. The reference point is used for S-GWrelocation due to UE mobility and if the S-GW needs to connect to anon-collocated PDN GW for required PDN connectivity S11 A referencepoint between the MME and the S-GW SGi A reference point between the PDNGW and the PDN. The PDN may be a public or private PDN external to anoperator or may be an intra-operator PDN, e.g., for the providing of IMSservices. This reference point corresponds to Gi for 3GPP access. Rx Areference point between PCRF and AF (Application Function), AF can beP-CSCF of IMS nework

Among the reference points shown in FIG. 1, S2 a and S2 b correspond toa Non-3GPP interface. S2 a is a reference point that provides the userplane with the relevant control and mobility support between trustedNon-3GPP access and PDN GW. S2 b is a reference point providing the userplane with the associated control and mobility support between the ePDGand the PDN GW.

FIG. 2 is an exemplary diagram showing the architecture of a commonE-UTRAN and a common EPC.

As shown in FIG. 2, the eNodeB 20 can perform functions, such as routingto a gateway while RRC connection is activated, the scheduling andtransmission of a paging message, the scheduling and transmission of abroadcast channel (BCH), the dynamic allocation of resources to UE inuplink and downlink, a configuration and providing for the measurementof the eNodeB 20, control of a radio bearer, radio admission control,and connection mobility control. The EPC can perform functions, such asthe generation of paging, the management of an LTE_IDLE state, theciphering of a user plane, control of an EPS bearer, the ciphering ofNAS signaling, and integrity protection.

FIG. 3 is an exemplary diagram showing the structure of a radiointerface protocol in a control plane between UE and an eNodeB, and FIG.4 is another exemplary diagram showing the structure of a radiointerface protocol in a control plane between UE and an eNodeB.

The radio interface protocol is based on a 3GPP radio access networkstandard. The radio interface protocol includes a physical layer, a datalink layer, and a network layer horizontally, and it is divided into auser plane for the transmission of information and a control plane forthe transfer of a control signal (or signaling).

The protocol layers may be classified into a first layer (L1), a secondlayer (L2), and a third layer (L3) based on three lower layers of theOpen System Interconnection (OSI) reference model that is widely knownin communication systems.

The layers of the radio protocol of the control plane shown in FIG. 3and the radio protocol in the user plane of FIG. 4 are described below.

The physical layer PHY, that is, the first layer, provides informationtransfer service using physical channels. The PHY layer is connected toa Medium Access Control (MAC) layer placed in a higher layer through atransport channel, and data is transferred between the MAC layer and thePHY layer through the transport channel. Furthermore, data istransferred between different PHY layers, that is, PHY layers on thesender side and the receiver side, through the PHY layer.

A physical channel is made up of multiple subframes on a time axis andmultiple subcarriers on a frequency axis. Here, one subframe is made upof a plurality of symbols and a plurality of subcarriers on the timeaxis. One subframe is made up of a plurality of resource blocks, and oneresource block is made up of a plurality of symbols and a plurality ofsubcarriers. A Transmission Time Interval (TTI), that is, a unit timeduring which data is transmitted, is 1 ms corresponding to one subframe.

In accordance with 3GPP LTE, physical channels that are present in thephysical layer of the sender side and the receiver side can be dividedinto a Physical Downlink Shared Channel (PDSCH) and a Physical UplinkShared Channel (PUSCH), that is, data channels, and a Physical DownlinkControl Channel (PDCCH), a Physical Control Format Indicator Channel(PCFICH), a Physical Hybrid-ARQ Indicator Channel (PHICH), and aPhysical Uplink Control Channel (PUCCH), that is, control channels.

A PCFICH that is transmitted in the first OFDM symbol of a subframecarries a Control Format Indicator (CFI) regarding the number of OFDMsymbols (i.e., the size of a control region) used to send controlchannels within the subframe. A wireless device first receives a CFI ona PCFICH and then monitors PDCCHs.

Unlike a PDCCH, a PCFICH is transmitted through the fixed PCFICHresources of a subframe without using blind decoding.

A PHICH carries positive-acknowledgement (ACK)/negative-acknowledgement(NACK) signals for an uplink (UL) Hybrid Automatic Repeat reQuest(HARQ). ACK/NACK signals for UL data on a PUSCH that is transmitted by awireless device are transmitted on a PHICH.

A Physical Broadcast Channel (PBCH) is transmitted in four former OFDMsymbols of the second slot of the first subframe of a radio frame. ThePBCH carries system information that is essential for a wireless deviceto communicate with an eNodeB, and system information transmittedthrough a PBCH is called a Master Information Block (MIB). In contrast,system information transmitted on a PDSCH indicated by a PDCCH is calleda System Information Block (SIB).

A PDCCH can carry the resource allocation and transport format of adownlink-shared channel (DL-SCH), information about the resourceallocation of an uplink shared channel (UL-SCH), paging information fora PCH, system information for a DL-SCH, the resource allocation of anupper layer control message transmitted on a PDSCH, such as a randomaccess response, a set of transmit power control commands for pieces ofUE within a specific UE group, and the activation of a Voice overInternet Protocol (VoIP). A plurality of PDCCHs can be transmittedwithin the control region, and UE can monitor a plurality of PDCCHs. APDCCH is transmitted on one Control Channel Element (CCE) or anaggregation of multiple contiguous CCEs. A CCE is a logical allocationunit used to provide a PDCCH with a coding rate according to the stateof a radio channel. A CCE corresponds to a plurality of resource elementgroups. The format of a PDCCH and the number of bits of a possible PDCCHare determined by a relationship between the number of CCEs and a codingrate provided by CCEs.

Control information transmitted through a PDCCH is called DownlinkControl Information (DCI). DCI can include the resource allocation of aPDSCH (also called a downlink (DL) grant)), the resource allocation of aPUSCH (also called an uplink (UL) grant), a set of transmit powercontrol commands for pieces of UE within a specific UE group, and/or theactivation of a Voice over Internet Protocol (VoIP).

Several layers are present in the second layer. First, a Medium AccessControl (MAC) layer functions to map various logical channels to varioustransport channels and also plays a role of logical channel multiplexingfor mapping multiple logical channels to one transport channel. The MAClayer is connected to a Radio Link Control (RLC) layer, that is, ahigher layer, through a logical channel. The logical channel isbasically divided into a control channel through which information ofthe control plane is transmitted and a traffic channel through whichinformation of the user plane is transmitted depending on the type oftransmitted information.

The RLC layer of the second layer functions to control a data size thatis suitable for sending, by a lower layer, data received from a higherlayer in a radio section by segmenting and concatenating the data.Furthermore, in order to guarantee various types of QoS required byradio bearers, the RLC layer provides three types of operation modes: aTransparent Mode (TM), an Un-acknowledged Mode (UM), and an AcknowledgedMode (AM). In particular. AM RLC performs a retransmission functionthrough an Automatic Repeat and Request (ARQ) function for reliable datatransmission.

The Packet Data Convergence Protocol (PDCP) layer of the second layerperforms a header compression function for reducing the size of an IPpacket header containing control information that is relatively large insize and unnecessary in order to efficiently send an IP packet, such asIPv4 or IPv6, in a radio section having a small bandwidth when sendingthe IP packet. Accordingly, transmission efficiency of the radio sectioncan be increased because only essential information is transmitted inthe header part of data. Furthermore, in an LTE system, the PDCP layeralso performs a security function. The security function includesciphering for preventing the interception of data by a third party andintegrity protection for preventing the manipulation of data by a thirdparty.

A Radio Resource Control (RRC) layer at the highest place of the thirdlayer is defined only in the control plane and is responsible forcontrol of logical channels, transport channels, and physical channelsin relation to the configuration, re-configuration, and release of RadioBearers (RBs). Here, the RB means service provided by the second layerin order to transfer data between UE and an E-UTRAN.

If an RRC connection is present between the RRC layer of UE and the RRClayer of a wireless network, the UE is in an RRC_CONNECTED state. Ifnot, the UE is in an RRC_IDLE state.

An RRC state and an RRC connection method of UE are described below. TheRRC state means whether or not the RRC layer of UE has been logicallyconnected to the RRC layer of an E-UTRAN. If the RRC layer of UE islogically connected to the RRC layer of an E-UTRAN, it is called theRRC_CONNECTED state. If the RRC layer of UE is not logically connectedto the RRC layer of an E-UTRAN, it is called the RRC_IDLE state. SinceUE in the RRC_CONNECTED state has an RRC connection, an E-UTRAN cancheck the existence of the UE in a cell unit, and thus control the UEeffectively. In contrast, if UE is in the RRC_IDLE state, an E-UTRANcannot check the existence of the UE, and a core network is managed in aTracking Area (TA) unit, that is, an area unit greater than a cell. Thatis, only the existence of UE in the RRC_IDLE state is checked in an areaunit greater than a cell. In such a case, the UE needs to shift to theRRC_CONNECTED state in order to be provided with common mobilecommunication service, such as voice or data. Each TA is classifiedthrough Tracking Area Identity (TAI). UE can configure TAI throughTracking Area Code (TAC), that is, information broadcasted by a cell.

When a user first turns on the power of UE, the UE first searches for aproper cell, establishes an RRC connection in the corresponding cell,and registers information about the UE with a core network. Thereafter,the UE stays in the RRC_IDLE state. The UE in the RRC_IDLE state(re)selects a cell if necessary and checks system information or paginginformation. This process is called camp on. When the UE in the RRC_IDLEstate needs to establish an RRC connection, the UE establishes an RRCconnection with the RRC layer of an E-UTRAN through an RRC connectionprocedure and shifts to the RRC_CONNECTED state. A case where the UE inthe RRC_IDLE state needs to establish with an RRC connection includesmultiple cases. The multiple cases may include, for example, a casewhere UL data needs to be transmitted for a reason, such as a callattempt made by a user and a case where a response message needs to betransmitted in response to a paging message received from an E-UTRAN.

A Non-Access Stratum (NAS) layer placed over the RRC layer performsfunctions, such as session management and mobility management.

The NAS layer shown in FIG. 3 is described in detail below.

Evolved Session Management (ESM) belonging to the NAS layer performsfunctions, such as the management of default bearers and the managementof dedicated bearers, and ESM is responsible for control that isnecessary for UE to use PS service from a network. Default bearerresources are characterized in that they are allocated by a network whenUE first accesses a specific Packet Data Network (PDN) or accesses anetwork. Here, the network allocates an IP address available for UE sothat the UE can use data service and the QoS of a default bearer. LTEsupports two types of bearers: a bearer having Guaranteed Bit Rate (GBR)QoS characteristic that guarantees a specific bandwidth for thetransmission and reception of data and a non-GBR bearer having the besteffort QoS characteristic without guaranteeing a bandwidth. A defaultbearer is assigned a non-GBR bearer, and a dedicated bearer may beassigned a bearer having a GBR or non-GBR QoS characteristic.

In a network, a bearer assigned to UE is called an Evolved PacketService (EPS) bearer. When assigning an EPS bearer, a network assignsone ID. This is called an EPS bearer ID. One EPS bearer has QoScharacteristics of a Maximum Bit Rate (MBR) and a Guaranteed Bit Rate(GBR) or an Aggregated Maximum Bit Rate (AMBR).

FIG. 5 illustrates a connection process in a radio resource control(RRC) layer.

FIG. 5 shows an RRC state depending on whether there is an RRCconnection. The RRC state denotes whether the entity of the RRC layer ofUE 10 is in logical connection with the entity of the RRC layer ofeNodeB 20, and if yes, it is referred to as RRC connected state, and ifno as RRC idle state.

In the connected state, UE 10 has an RRC connection, and thus, theE-UTRAN may grasp the presence of the UE on a cell basis and may thuseffectively control UE 10. In contrast, UE 10 in the idle state cannotgrasp eNodeB 20 and is managed by a core network on the basis of atracking area that is larger than a cell. The tracking area is a set ofcells. That is, UE 10 in the idle state is grasped for its presence onlyon a larger area basis, and the UE should switch to the connected stateto receive a typical mobile communication service such as voice or dataservice.

When the user turns on UE 10, UE 10 searches for a proper cell and staysin idle state in the cell. UE 10, when required, establishes an RRCconnection with the RRC layer of eNodeB 20 through an RRC connectionprocedure and transits to the RRC connected state.

There are a number of situations where the UE staying in the idle stateneeds to establish an RRC connection, for example, when the userattempts to call or when uplink data transmission is needed, or whentransmitting a message responsive to reception of a paging message fromthe EUTRAN.

In order for the idle UE 10 to be RRC connected with eNodeB 20, UE 10needs to perform the RRC connection procedure as described above. TheRRC connection procedure generally comes with the process in which UE 10transmits an RRC connection request message to eNodeB 20, the process inwhich eNodeB 20 transmits an RRC connection setup message to UE 10, andthe process in which UE 10 transmits an RRC connection setup completemessage to eNodeB 20. The processes are described in further detail withreference to FIG. 6.

1) The idle UE 10, when attempting to establish an RRC connection, e.g.,for attempting to call or transmit data or responding to paging fromeNodeB 20, sends an RRC connection request message to eNodeB 20.

2) When receiving the RRC connection message from UE 10, eNodeB 20accepts the RRC connection request from UE 10 if there are enough radioresources, and eNodeB 20 sends a response message. RRC connection setupmessage, to UE 10.

3) When receiving the RRC connection setup message, UE 10 transmits anRRC connection setup complete message to eNodeB 20. If UE 10successfully transmits the RRC connection setup message, UE 10 happensto establish an RRC connection with eNodeB 20 and switches to the RRCconnected state.

FIG. 6 shows a connection between an EPC and an IP multimedia subsystem(IMS).

Referring to FIG. 6, the EPC includes an MME 51, an S-GW 52, a P-GW 53 ato be coupled to the IMS, a P-GW 53 b to be coupled to the Internet, anda policy and charging rule function (PCRF) 58 to be coupled to the P-GW53 a.

A network technology which enables up to a wireless terminal to performpacket switching (PS) based on an Internet protocol (IP) is proposed toconnect both wired/wireless terminals through all-IPs.

A network based on the IMS includes a call session control function(CSCF) for control signaling, registration, and cession processing and asession and interconnection border control function (IBCF) 62. The CSCFmay include a proxy-CSCF (P-CSCF) 61 and an S-CSCF (Serving-CSCF) 63. Inaddition, the CSCF may include an interrogating-CSCF (I-CSCF). TheP-CSCF 61 acts as a first access point for a user equipment (UE) in theIMS-based network. In addition, the S-CSCF 63 processes a session in theIMS network. That is, the S-SCSF 63 is an entity which is in charge ofrouting signaling, and routes the session in the IMS network. Inaddition, the I-CSCF acts as an access point with respect to anotherentity within the IMS network.

An IP-based session is controlled by a session initiation protocol (SIP)under the IMS. The SIP is a protocol for controlling the session. TheSIP is a signaling protocol which specifies a procedure for findinglocations by identifying UEs to be communicated, generating a multimediaservice session between the UEs, and deleting and changing the generatedsession. The SIP uses an SIP uniform resource identifier (URI) similarto an e-mail address to distinguish each user, so that a service can beprovided without being dependent on an Internet protocol (IP) address.The SIP message is a control message, but is transmitted between the UEand the IMS network through an EPC user plane.

Referring to FIG. 6, the first P-GW 53 a of the EPC is coupled to theP-CSCF 61 of the IMS, the P-CSCF 61 is coupled to the IBCF 62, and theIBCF 62 is coupled to the S-CSCF 63.

In addition, the second P-GW 53 b of the EPC is coupled to a network ofthe Internet service operator.

Hereinafter, an initial access procedure of the UE 10 is described.

According to the initial access procedure, the EPC may allocate adefault bearer to the UE 10, and may register the UE 10. In addition,the UE 10 may be allocated an IP address to use an IMS network from thePGW 53, and may obtain an address of the P-CSCF 61 to register to an IMSnetwork.

FIG. 7 is an exemplary signal flow diagram showing an initial accessprocedure of a UE.

Referring to FIG. 7, for an initial access, the UE 10 which has beenpowered on configures an RRC connection with the eNodeB 20 as describedwith reference to FIG. 5 (S101).

After the RRC connection with the eNodeB 20 is established, the UE 10transmits an attach request message to the MME 51 (S103). A PDNconnectivity request message may be included in the attach requestmessage. In this case, the UE 10 may request for an address of theP-CSCF 61 by using a protocol configuration option (PCO) field.

The MME 51 performs an authentication and security setup procedure forthe UE 10 in association with the HSS 54 (S105). In the authenticationprocedure, the MME 51 obtains an authentication vector for a subscriberfrom the HSS 54, and thereafter performs mutual authentication withrespect to the UE 10 by using the authentication vector. When theauthentication procedure is complete, the MME 51 establishes a securitykey for the message security setup between the UE 10 and the MME 51.

The MME 51 performs a location registration procedure to inform the HSS54 that the UE 10 is located in a region managed by the MME 51, andreceives a user profile (S107). The location registration procedure maybe performed by using a diameter protocol on an S6 a interface. Inaddition, the user profile received by the MME 51 may include an accesspoint name (APN), a P-GW identifier, a quality of service (QoS) profile,or the like.

The MME 51 selects the P-GW 53, and transmits a create session requestmessage to the selected P-GW 53 (S109). The create session requestmessage may include the user profile and the PCO field requesting anaddress of the P-CSCF 61. The create session request message transmittedby the MME 51 may be delivered to the P-GW 53 via the S-GW 52.

The P-GW 53 allocates the IP of the UE 10, and selects an address listof the P-CSCFs 61 which can be used by the UE among a plurality ofP-CSCFs 61 according to the PCO field. Optionally, the P-GW 53 transmitsan ‘indication of IP-CAN session establishment’ message to the PCRF 58(S111). In addition, the P-GW 53 receives an ‘acknowledge of IP-CONsession establishment’ message from the PCRF 58 (S113). The ‘acknowledgeof IP-CON session establishment’ message may include a policy of aservice to be provided to the UE 10.

The P-GW 53 transmits a create session response message to the MME 51(S115). The create session response message may include an IP allocatedto the UE 10 and the address list of the P-CSCF 61. The create sessionresponse message transmitted by the P-GW 53 may be transmitted to theMME 51 via the S-GW 52.

The MME 51 transmits an attach accept message including an initialcontext setup request message to the eNodeB 20. In addition, the eNodeB20 transmits to the UE an access accept message including an RRCconnection reconfiguration message and an activate default EPS bearercontext request message (S117).

In step S119, the UE 10 transmits an RRC connection reconfigurationcomplete message to the eNodeB 20 in response to reception of the RRCconnection reconfiguration message (S119). The eNodeB 20 transmits aninitial context setup response message to the MME 51 in response toreception of the initial context setup request message (S121).

The MME 51 transmits a modify bearer request message to the S-GW 52 inresponse to reception of the initial context setup response message(S123). The bearer modify request message may include an EPS beareridentifier, an eNodeB address, a handover indication, or the like. TheS-GW 52 transmits a modify bearer response message to the MME 51 inresponse to reception of the modify bearer response message (S125).

Hereinafter, an IMS initial registration procedure of the UE 10 will bedescribed.

FIG. 8 is an exemplary signal flow diagram showing an IMS initialregistration procedure.

Referring to FIG. 8, the UE 10 transmits a register message requestingfor a registration to the P-CSCF 61 (S201). The UE 10 may transmit aregister message by using an address of the P-CSCF 61, which isidentified through the activate default EPS bearer context requestmessage.

The P-CSCF 61 delivers the register message received from the UE 10 tothe I-CSCF 64 by using an address of the I-CSCF 64, which is obtainedthrough a domain name system (DNS) query procedure (S203).

The I-CSCF 64 transmits a user authorization request (UAR) message tothe HSS 54 (S205). Since there is no S-CSCF 63 allocated to the UE 10,the HSS 54 transmits to the I-CSCF 64 a user authorization answer (UAA)message including capability information of the UE 10 (S207). Thecapability information is information in which capability to be providedto the UE 10 is organized with an attribute value pair (AVP).

The I-CSCF 64 selects one S-CSCF 63 on the basis of the receivedcapability information, and transmits a register message to the selectedS-CSCF 63 (S209).

The S-CSCF 63 transmits a multimedia authentication request (MAR)message to the HSS 54 to request for authentication informationregarding the UE 10 (S211). Since there is no authentication informationregarding the UE 10 due to the IMS initial registration, the HSS 54transmits a multimedia authentication answer (MAA) message for informingthat the authentication information is required to the S-CSCF 63 (S213).

The S-CSCF 63 transmits a 401 unauthorized message for requesting forthe authentication information to the UE 10 (S215). The 401 unauthorizedmessage may include an authentication vector received from the HSS, asymmetric key designated by the S-CSCF 63, and an authenticationalgorithm. The 401 unauthorized message may be delivered to the UE 10via the I-CSCF 64 and the P-CSCF 61.

The UE 10 generates authentication data by using the receivedauthentication vector, symmetric key, and authentication algorithm, andtransmits the register message including the generated authenticationdata to the P-CSCF 61 (S217). The P-CSCF 61 delivers the receivedregister message to the I-CSCF 64 (S219).

The I-CSCF 64 transmits the UAR message to the HSS 54 (S221). Since theS-CSCF 63 allocated to the UE 10 exists, the HSS 54 transmits the UAAmessage including the identification information of the allocated S-CSCF63 to the I-CSCF 64 since (S223). The I-CSCF 64 transmits the registermessage to the S-CSCF 63 (S225).

The S-CSCF 63 authenticates the UE 10 by comparing authentication dataincluded in the register message and authentication informationtransmitted by the S-CSCF 63, and transmits a server assignment request(SAR) message to the HSS (S227). The HSS 54 transmits to the S-CSCF 63 aserver assignment answer (SAA) message including a service profile forthe UE 10 (S229).

The S-CSCF 63 transmits to the UE 10 a 200 OK message notifying that theregistration is complete, thereby completing the registration procedure(S231). The 200 OK message may be delivered to the UE 100 via the I-CSCF64 and the P-CSCF 61.

FIG. 9 is an exemplary diagram showing a roaming scheme of voice overLTE (VoLTE).

As can be seen with reference to FIG. 9, the roaming scheme of VoLTEincludes a home routed (HR) scheme and a local breakout (LBO) scheme.

According to the LBO scheme, IMS signaling transmitted from a UE isdelivered to an S-CSCF in a home PLMN (H-PLMN) via an S-GW/P-GW/P-CSCFin a visited public land mobile network (V-PLMN).

In the HR scheme, the IMS signaling is delivered to the S-CSCF afterpassing through a P-GW/P-CSCF in the H-PLMH via the S-GW in the V-PLMN.

FIG. 10 is an exemplary signal flow diagram showing an IMS registrationprocedure of a UE roamed to a visited network through an HR scheme.

Hereinafter, when the IMS registration procedure based on the HR schemeof the UE 10 roamed to the visited network through the HR scheme isdescribed, the duplicated description of FIG. 8 will be omitted.

Referring to FIG. 10, the UE 10 roamed to a visited network (or V-PLMN)transmits a register message to the S-GW 52 b of the visited network viaan eNB. The S-GW 52 b of the visited network transmits the receivedregister message to the P-GW 53 a of a home network, and the P-GW 53 atransmits the received register message to the P-CSCF 61 a (S301). Thatis, the UE 10 transmits the register message to not a control plane buta user plane.

The P-CSCF 61 a subscribes a network identifier (or PLMN-ID) changenotification to the PCRF 58 a (S303). In this case, the PLMN-ID changenotification may be subscribed through an Rx interface. The Rx interfaceis an interface for exchanging information between the P-CSCF 61 a of anIMS network and the PCRF 58 a of an EPC network.

The PCRF 58 a configures the P-GW 53 a to report the PLMN-ID change(S305). In addition, the P-GW 53 a reports a PLMN-ID for the network(i.e., the V-PLMN) serving the UE 10 to the PCRF 58 a on the basis ofinformation obtained in the PDN setup process (S307). As the PLMN-IDchange notification is subscribed for the first time, the PCRF 58 areports the PLMN-ID for the V-PLMN to the P-CSCF 61 a (S309).

That is, entities of the home network acquire an identifier of thevisited network (or VPLMN-ID) in an IMS registration procedure. TheVPLMN-ID acquired in this manner may be used in charging, roamingregistration restriction, or bear creation for an additional service, orthe like.

The P-CSCF 61 a adds the PLMN-ID to a P-visited-network-ID header of theregister message, and delivers to the I-CSCF 64 a the register messageto which the PLMN-ID is added (S311).

In addition, a subsequent IMS registration procedure is performed in thesame manner as described with reference to FIG. 8.

Meanwhile, when the network serving the UE 10 is changed due to amovement of the UE 10, the P-GW 53 a of the home network may identify achange of the PLMN-ID. Upon identifying the change of the PLMN-ID, theP-GW 53 a reports to the PCRF 58 a an event occurrence based on thePLMN-ID change. Upon receiving the report of the event occurrence basedon the PLMN-ID change, the PCRF 58 a reports a new PLMN-ID to the P-CSCF61 a.

Meanwhile, it is preferable that the Rx interface for exchanginginformation between the P-CSCF and the PCRF is generated after theauthentication of the UE 10 is successfully performed in the IMSregistration procedure.

However, as described above with reference to FIG. 10, before the UE 10is authenticated, the IMS registration procedure of the HR schemegenerates the Rx interface between the P-CSCF and the PCRF to subscribethe PLMN-ID change notification.

As such, when the Rx interface is generated before the UE 10 isauthenticated, the information regarding the unregistered UE 10 isexchanged between entities of the home network, which may cause aproblem in terms of security.

In addition, even if the IMS registration procedure fails, unnecessarysignaling such as the PLMN-ID change notification may occur through anRx interface which is already activated.

SUMMARY OF THE INVENTION

Accordingly, a disclosure of the present specification aims to provide amethod of effectively acquiring a visited public land mobile network(V-PLMN)-identifier (ID) when an IP multimedia subsystem (IMS)registration is performed for a user equipment (UE) roamed through ahome routed (HR) scheme.

To achieve the above purpose, a disclosure of the present specificationprovides a method for obtaining an identifier of a V-PLMN in order toregister a UE, which has roamed to the V-PLMN, to an IMS network. Themethod may be performed by a proxy-call session control function(P-CSCF). The method may include: receiving a response message from aninterrogating-CSCF (I-CSCF) in response to transmission of a registermessage for registering the UE to the IMS network; verifying whether thereceived response message is a 401 unauthorized message; when thereceived response message is the 401 unauthorized message, transmittingthe response message to the UE, and generating an interface fortransmitting and receiving data with respect to an entity of an EPCnetwork; and receiving the identifier of the V-PLMN from the entity ofthe EPC through the interface.

The method may further include, if a new register message is receivedfrom the UE, transmitting the new register message to the I-CSCF byadding the identifier of the V-PLMN to a header of the new registermessage.

In the receiving of the identifier of the V-PLMN, a notification for achange in the identifier of the V-PLMN may be subscribed for the entityof the EPC network through the interface, and the identifier of theV-PLMN may be received from the entity of the EPC network.

If the entity of the EPC network is a policy and charging rule function(PCRF), the interface may be a reception (Rx) reference point.

To achieve the above purpose, another disclosure of the presentspecification provides a method for obtaining an identifier of a V-PLMNin order to register a UE, which has roamed to the V-PLMN, to an IMSnetwork. The method may be performed by a proxy-call session controlfunction (P-CSCF). The method may include: when a register message isreceived from the UE to request for a registration to the IMS, holdingthe received register message and generating a temporary registermessage; transmitting the generated temporary register message to anI-CSCF, and receiving a response message; verifying whether the responsemessage is a message for allowing the UE to be registered to the IMSnetwork; when the received response message is the message for allowingthe registration to the IMS network, discarding the response message,and generating an interface for transmitting/receiving data with respectto an entity of an EPC network; and receiving the identifier of theV-PLMN from the entity of the EPC through the interface.

The method may further include transmitting the register message to theI-CSCF by adding the identifier of the V-PLMN to a header of the heldregister message.

The message for allowing the registration to the IMS network may be anyone of a 401 unauthorized message and a 200 OK message.

To achieve the above purpose, another disclosure of the presentspecification provides a P-CSCF for obtaining an identifier of a V-PLMNin order to register a UE, which has roamed to the V-PLMN, to an IMSnetwork. The P-CSCF may include: a transceiver; and a processorcontrolling the transceiver. The processor is configured to: control thetransceiver to receive a response message from an I-CSCF in response totransmission of a register message for registering the UE to the IMSnetwork; verify whether the received response message is a 401unauthorized message; control the transceiver to transmit the responsemessage to the UE and generate an interface for transmitting andreceiving data with respect to an entity of an EPC network, when thereceived response message is the 401 unauthorized message; and controlthe transceiver to receive the identifier of the V-PLMN from the entityof the EPC through the interface.

To achieve the above purpose, another disclosure of the presentspecification provides a P-CSCF for obtaining an identifier of a V-PLMNin order to register a UE, which has roamed to the V-PLMN, to an IMSnetwork. The P-CSCF may include: a transceiver; and a processorcontrolling the transceiver. The processor may be configured to: holdthe received register message and generate a temporary register messagewhen a register message is received from the UE to request for aregistration to the IMS; control the transceiver to transmit thegenerated temporary register message to an I-CSCF, and receive aresponse message; verify whether the response message is a message forallowing the UE to be registered to the IMS network; control thetransceiver to discarding the response message, and generate aninterface for transmitting/receiving data with respect to an entity ofan EPC network, when the received response message is the message forallowing the registration to the IMS network; and control thetransceiver to receive the identifier of the V-PLMN from the entity ofthe EPC through the interface.

According to a disclosure of the present specification, since a visitedpublic land mobile network (V-PLMN)-identifier (ID) is acquired througha reception (Rx) interface generated after a user equipment (UE) isauthenticated in an IP multimedia subsystem (IMS) registrationprocedure, it is possible to solve a problem in which entities of a homenetwork exchange information regarding an unregistered UE.

In addition, since the Rx interface is not generated when the IMSregistration procedure fails, it is possible to solve a problem in whichunnecessary signaling occurs between the entities of the home network.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the configuration of an evolved mobile communicationnetwork.

FIG. 2 is an exemplary diagram showing the architecture of a commonE-UTRAN and a common EPC.

FIG. 3 is an exemplary diagram showing the structure of a radiointerface protocol in a control plane between UE and an eNodeB

FIG. 4 is another exemplary diagram showing the structure of a radiointerface protocol in a control plane between UE and an eNodeB.

FIG. 5 illustrates a connection process in a radio resource control(RRC) layer.

FIG. 6 shows a connection between an EPC and an IP multimedia subsystem(IMS).

FIG. 7 is an exemplary signal flow diagram showing an initial accessprocedure of a UE.

FIG. 8 is an exemplary signal flow diagram showing an IMS initialregistration procedure.

FIG. 9 is an exemplary diagram showing a roaming scheme of voice overLTE (VoLTE).

FIG. 10 is an exemplary signal flow diagram showing an IMS registrationprocedure of a UE roamed to a visited network through an HR scheme.

FIG. 11 to FIG. 14 are signal flow diagrams showing first to fourthschemes according to a disclosure of the present specification.

FIG. 15 is a flowchart showing a method in which a P-CSCF performs thefirst scheme according to a disclosure of the present specification.

FIG. 16 is a flowchart showing a method in which a P-CSCF performs thesecond scheme according to a disclosure of the present specification.

FIG. 17 is a block diagram showing a structure of a UE and a P-CSCFaccording to a disclosure of the present specification.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

The present invention is described in light of UMTS (Universal MobileTelecommunication System) and EPC (Evolved Packet Core), but not limitedto such communication systems, and may be rather applicable to allcommunication systems and methods to which the technical spirit of thepresent invention may apply.

The technical terms used herein are used to merely describe specificembodiments and should not be construed as limiting the presentinvention. Further, the technical terms used herein should be, unlessdefined otherwise, interpreted as having meanings generally understoodby those skilled in the art but not too broadly or too narrowly.Further, the technical terms used herein, which are determined not toexactly represent the spirit of the invention, should be replaced by orunderstood by such technical terms as being able to be exactlyunderstood by those skilled in the art. Further, the general terms usedherein should be interpreted in the context as defined in thedictionary, but not in an excessively narrowed manner.

The expression of the singular number in the specification includes themeaning of the plural number unless the meaning of the singular numberis definitely different from that of the plural number in the context.In the following description, the term ‘include’ or ‘have’ may representthe existence of a feature, a number, a step, an operation, a component,a part or the combination thereof described in the specification, andmay not exclude the existence or addition of another feature, anothernumber, another step, another operation, another component, another partor the combination thereof.

The terms ‘first’ and ‘second’ are used for the purpose of explanationabout various components, and the components are not limited to theterms ‘first’ and ‘second’. The terms ‘first’ and ‘second’ are only usedto distinguish one component from another component. For example, afirst component may be named as a second component without deviatingfrom the scope of the present invention.

It will be understood that when an element or layer is referred to asbeing “connected to” or “coupled to” another element or layer, it can bedirectly connected or coupled to the other element or layer orintervening elements or layers may be present. In contrast, when anelement is referred to as being “directly connected to” or “directlycoupled to” another element or layer, there are no intervening elementsor layers present.

Hereinafter, exemplary embodiments of the present invention will bedescribed in greater detail with reference to the accompanying drawings.In describing the present invention, for ease of understanding, the samereference numerals are used to denote the same components throughout thedrawings, and repetitive description on the same components will beomitted. Detailed description on well-known arts which are determined tomake the gist of the invention unclear will be omitted. The accompanyingdrawings are provided to merely make the spirit of the invention readilyunderstood, but not should be intended to be limiting of the invention.It should be understood that the spirit of the invention may be expandedto its modifications, replacements or equivalents in addition to what isshown in the drawings.

In the drawings, user equipments (UEs) are shown for example. The UE mayalso be denoted a terminal or mobile equipment (ME). The UE may be alaptop computer, a mobile phone, a PDA, a smartphone, a multimediadevice, or other portable device, or may be a stationary device such asa PC or a car mounted device.

<Definition of Terms>

For a better understanding, the terms used herein are briefly definedbefore going to the detailed description of the invention with referenceto the accompanying drawings.

A GERAN is an abbreviation of a GSM EDGE Radio Access Network, and itrefers to a radio access section that connects a core network and UE byGSM/EDGE.

A UTRAN is an abbreviation of a Universal Terrestrial Radio AccessNetwork, and it refers to a radio access section that connects the corenetwork of the 3rd generation mobile communication and UE.

An E-UTRAN is an abbreviation of an Evolved Universal Terrestrial RadioAccess Network, and it refers to a radio access section that connectsthe core network of the 4th generation mobile communication, that is,LTE, and UE.

An UMTS is an abbreviation of a Universal Mobile TelecommunicationSystem, and it refers to the core network of the 3rd generation mobilecommunication.

UE or an MS is an abbreviation of User Equipment or a Mobile Station,and it refers to a terminal device.

An EPS is an abbreviation of an Evolved Packet System, and it refers toa core network supporting a Long Term Evolution (LTE) network and to anetwork evolved from an UMTS.

A PDN is an abbreviation of a Public Data Network, and it refers to anindependent network where a service for providing service is placed.

A PDN connection refers to a connection from UE to a PDN, that is, anassociation (or connection) between UE represented by an IP address anda PDN represented by an APN.

A PDN-GW is an abbreviation of a Packet Data Network Gateway, and itrefers to a network node of an EPS network which performs functions,such as the allocation of a UE IP address, packet screening & filtering,and the collection of charging data.

A Serving gateway (Serving GW) is a network node of an EPS network whichperforms functions, such as mobility anchor, packet routing, idle modepacket buffering, and triggering an MME to page UE.

A Policy and Charging Rule Function (PCRF) is a node of an EPS networkwhich performs different QoS for each service flow and a policy decisionfor dynamically applying a charging policy.

An Access Point Name (APN) is the name of an access point that ismanaged in a network and provides to UE. That is, an APN is a characterstring that denotes or identifies a PDN. Requested service or a network(PDN) is accessed via a P-GW. An APN is a name (character string, e.g.,‘internet.mnc012.mcc345.gprs’) previously defined within a network sothat the P-GW can be searched for.

A Tunnel Endpoint Identifier (TEID) is an end point ID of a tunnel setup between nodes within a network and is set in each section as a bearerunit of each terminal.

A NodeB is an eNodeB of a UMTS network and installed outdoors. The cellcoverage of the NodeB corresponds to a macro cell.

An eNodeB is an eNodeB of an Evolved Packet System (EPS) and isinstalled outdoors. The cell coverage of the eNodeB corresponds to amacro cell.

An (e)NodeB is a term that denotes a NodeB and an eNodeB.

An MME is an abbreviation of a Mobility Management Entity, and itfunctions to control each entity within an EPS in order to provide asession and mobility for UE.

A session is a passage for data transmission, and a unit thereof may bea PDN, a bearer, or an IP flow unit. The units may be classified into aunit of the entire target network (i.e., an APN or PDN unit) as definedin 3GPP, a unit (i.e., a bearer unit) classified based on QoS within theentire target network, and a destination IP address unit.

A PDN connection is a connection from UE to a PDN, that is, anassociation (or connection) between UE represented by an IP address anda PDN represented by an APN. It means a connection between entities(i.e., UE-PDN GW) within a core network so that a session can be formed.

UE context is information about the situation of UE which is used tomanage the UE in a network, that is, situation information including anUE ID, mobility (e.g., a current location), and the attributes of asession (e.g., QoS and priority)

A Non-Access-Stratum (NAS) is a higher stratum of a control planebetween UE and an MME. The NAS supports mobility management and sessionmanagement between UE and a network, IP address maintenance, and so on.

RAT is an abbreviation of Radio Access Technology, and it means a GERAN,a UTRAN, or an E-UTRAN.

Meanwhile, an embodiment proposed hereinafter may be implemented alone,or may be implemented by combining several embodiments.

<Disclosure of the Present Specification>

The present specification discloses a method of effectively obtaining avisited public land mobile network (V-PLMN)-identifier (ID) when an IMSregistration is performed on a UE which has roamed to a visited networkthrough an HR scheme. In particular, the present specification proposesa method of generating an Rx interface between a P-CSCF and a PCRF aftera minimum level of authentication is performed on the UE, when the IMSregistration is performed on the UE roamed to the visited networkthrough the HR scheme.

1. First Scheme According to a Disclosure of the Present Specification

The first scheme according to the disclosure of the presentspecification is a scheme of additionally performing a process ofidentifying whether an IMS registration of a UE can be allowed before anRx interface is generated between a P-CSCF and a PCRF. As such, theprocess of identifying whether the IMS registration of the UE can beallowed may be implemented by applying a message of the conventional IMSregistration procedure. Therefore, the process of identifying whetherthe IMS registration of the UE can be allowed is referred to as atemporary IMS registration procedure.

FIG. 11 is a signal flow diagram showing a first scheme according to adisclosure of the present specification.

Referring to FIG. 11, the UE 10 roamed to a visited network (or V-PLMN)transmits a register message for IMS registration (S401). The registermessage transmitted by the UE 10 may be delivered to the P-CSCF 61 a ofa home network via the S-GW 52 b of the visited network and the P-GW 53a of the home network through an HR scheme.

The P-CSCF 61 a preferentially performs the temporary IMS registrationprocedure before a PLMN-ID change notification is subscribed to the PCRF58 a. That is, in order to be configured to report the PLMN-ID change,an Rx interface is inevitably generated between the -CSCF 61 a and thePCRF 58 a. Therefore, the P-CSCF 61 a performs a minimum level ofauthentication on the UE 10 before the PLMN-ID change notification issubscribed to the PCRF 58 a.

More specifically, the P-CSCF 61 a holds a register message receivedfrom the UE 10, and transmits a temporary register message autonomouslygenerated to the I-CSCF 64 a (S403). If it is determined that the UE 10is in an HR-based roaming state on the basis of the register messagereceived from the UE, the P-CSCF 61 a may transmit the temporaryregister message by including an indicator for informing that the UE 100is in the HR-based roaming state. In addition, the P-CSCF 61 atemporarily stores the register message received from the UE 10 until aminimum level of authentication is performed on the UE.

The I-CSCF 64 a transmits a UAR message to the HSS 54 a (S405). Inparticular, the I-CSCF 64 a may transmit the UAR message by includingthe IP address of the UE 10.

The HSS 54 a identifies whether the IMS registration of the UE 10 isallowed based on an IP address and subscriber information of the UE 10included in the UAR message (S407). For this, the HSS 54 a may haveconfiguration information regarding a mapping relationship between thePLMN and an IP address pool. Alternatively, when the configurationinformation is required, the HSS 54 a may obtain the configurationinformation from another entity. The HSS 54 a may determine that the IMSregistration of the UE 10 is allowed when the IP address of the UE 10included in the UAR message is included in the IP address pool. When theIMS registration of the UE is allowed, the HSS 54 a transmits a UAAmessage to the I-CSCF 64 a (S409). Otherwise, when it is determined thatthe IMS registration of the UE 10 is not allowed, the HSS 54 a maytransmit a message for preventing the IMS registration of the UE 10 tothe P-CSCF 61 a. In this case, the P-CSCF 61 a may transmit an IMSregistration failure message to the UE 10.

The I-CSCF 64 a delivers the temporary register message to the S-CSCF 63a on the basis of the received UAA message (S411).

The S-CSCF 63 a transmits an MAR message to the HSS 54 a to request forauthentication information regarding the UE (S413). When the IMSregistration of the UE is allowed, the HSS 54 a transmits an MAA messageto the S-CSCF 63 a (S415).

When it is determined that the IMS registration of the UE 10 is allowedon the basis of the MAA message received from the HSS 54 a, the S-CSCF63 a transmits to the P-CSCF 61 a a message notifying that theauthentication of the UE 10 is allowed (S417). Herein, the messagenotifying that the authentication of the UE is allowed may be either a401 unauthorized message or a 200 OK message. However, the presentinvention is not limited thereto, and the message may a message obtainedby processing the 401 unauthorized message or the 200 OK message. Themessage notifying that the authentication of the UE 10 is allowed may bedelivered to the P-CSCF 61 a via the I-CSCF 64 a.

When the P-CSCF 61 a receives a message notifying that theauthentication of the UE 10 is allowed, the P-CSCF 61 a determines thata minimum level of authentication is performed on the UE 10, andgenerates an Rx interface. The P-CSCF 61 a subscribes a PLMN-ID changenotification to the PCRF 58 a through the generated Rx interface (S419).The P-CSCF 61 does not deliver to the UE 10 the message notifying thatthe authentication of the UE 10 is allowed. That is, in the firstscheme, the message notifying that authentication of the UE 10 isallowed serves as a trigger for generating the Rx interface.

According to the conventional IMS registration procedure, the P-CSCF 61a transmits the 401 unauthorized message received from the I-CSCF 64 ato the UE 10 without any processing, whereas the P-CSCF 61 a accordingto the first scheme needs to verify whether the PLMN-ID changenotification is subscribed to the RCPF 58 a on the basis of the 401unauthorized message received from the I-CSCF 64 a.

The PCRF 58 a configures the P-GW 53 a to report the PLMN-ID change(S421). The P-GW 53 a reports a PLMN-ID for a network (i.e., V-PLMN)serving the UE 10 to the PCRF 58 a (S423). In addition, the PCRF 58 areports the PLMN-ID for the V-PLMN to the P-CSCF 61 a (S425).

The P-CSCF 61 a adds the received PLMN-ID to a P-Visited-Network-IDheader of the held register message, and delivers it to the I-CSCF 64 a(S427).

In addition, a subsequent IMS registration procedure is performed in thesame manner as described with reference to FIG. 8.

2. Second Scheme According to a Disclosure of the Present Specification

The second scheme according to the disclosure of the presentspecification is a scheme of performing a minimum level ofauthentication on the UE 10 before an Rx interface is generated, byapplying the conventional IMS registration procedure without having toadditionally perform a temporary IMS registration procedure.

FIG. 12 is a signal flow diagram showing a second scheme according to adisclosure of the present specification.

Referring to FIG. 12, the UE 10 roamed to a visited network (or V-PLMN)transmits a register message for IMS registration (S501). The registermessage transmitted by the UE 10 may be delivered to the P-CSCF 61 a ofa home network via the S-GW 52 b of the visited network and the P-GW 53a of the home network through an HR scheme.

The P-CSCF 61 a transmits the register message received from the UE 10to the I-CSCF 64 a (S503). The I-CSCF 64 a transmits a UAR message tothe HSS 54 a (S505). In particular, the I-CSCF 64 a may transmit the UARmessage by including an IP address of the UE 10. The HSS 54 a identifieswhether the IMS registration of the UE 10 is allowed based on an IPaddress and subscriber information of the UE 10 included in the UARmessage (S507). For this, the HSS 54 a may have configurationinformation regarding a mapping relationship between the PLMN and an IPaddress pool. Alternatively, when the configuration information isrequired, the HSS 54 a may obtain the configuration information fromanother entity. The HSS 54 a may determine that the IMS registration ofthe UE 10 is allowed when the IP address of the UE 10 included in theUAR message is included in the IP address pool.

When the IMS registration of the UE is allowed, the HSS 54 a transmits aUAA message to the I-CSCF 64 a (S507). Otherwise, when it is determinedthat the IMS registration of the UE 10 is not allowed, the HSS 54 a maytransmit a message for preventing the IMS registration of the UE 10 tothe P-CSCF 61 a. In this case, the P-CSCF 61 a may transmit an IMSregistration failure message to the UE 10.

The I-CSCF 64 a transmits the register message received from the UE 10to the S-CSCF 63 a on the basis of the received UAA message (S509).

The S-CSCF 63 a transmits an MAR message to the HSS 54 a to request forauthentication information regarding the UE 10 (S511). Since there is noauthentication information for the UE 10 due to the IMS initialregistration, an MAA message for informing that the authenticationinformation is required is transmitted to the S-CSCF 63 a (S513).

The S-CSCF 63 a transmits a 401 unauthorized message for a request ofthe authentication information to the P-CSCF 61 a (S515). The 401unauthorized message may be delivered to the P-CSCF 61 a via the I-CSCF64 a.

Upon receiving the 401 unauthorized message, the P-CSCF 61 a transmitsthe 401 unauthorized message to the UE 10 (S517). In addition, theP-CSCF 61 a determines that a minimum level of authentication isperformed on the UE 10, and generates an Rx interface.

The P-CSCF 61 a subscribes a PLMN-ID change notification to the PCRF 58a through the generated Rx interface (S519). That is, in the secondscheme, the 401 unauthorized message acts as a trigger for generatingthe Rx interface.

The PCRF 58 a configures the P-GW 53 a to report the PLMN-ID change(S521). The P-GW 53 a reports the PLMN-ID for a network (i.e., V-PLMN)serving the UE 10 to the PCRF 58 a (S523). In addition, the PCRF 58 areports a PLMN-ID for the V-PLMN to the P-CSCF 61 a (S525).

When a new register message including authentication data is receivedfrom the UE 10 (S527), the PCRF 58 a adds the received PLMN-ID to aP-Visited-Network-ID header of the received register message, anddelivers it to the I-CSCF 64 a (S429).

In addition, a subsequent IMS registration procedure is performed in thesame manner as described with reference to FIG. 8.

3. Third Scheme According to a Disclosure of the Present Specification

The third scheme according to the disclosure of the presentspecification is a scheme in which a PCRF autonomously performs aminimum level of authentication on a UE while generating up to an Rxinterface in an IMS registration procedure.

FIG. 13 is a signal flow diagram showing a third scheme according to adisclosure of the present specification.

Referring to FIG. 13, the UE 10 roamed to a visited network (or V-PLMN)transmits a register message for IMS registration (S601). The registermessage transmitted by the UE 10 may be delivered to the P-CSCF 61 a ofa home network via the S-GW 52 b of the visited network and the P-GW 53a of the home network through an HR scheme.

The P-CSCF 61 a subscribes a network identifier (or PLMN-ID) changenotification to the PCRF 58 a (S603).

Upon receiving a request for subscribing a PLMN change notification, thePCRF 58 a verifies whether the IMS registration of the UE 10 is allowed(S605). Specifically, the PCRF 58 a may verify whether the IMSregistration is requested from the normal UE 10. In addition, the PCRF58 a may verify whether the IMS registration of the UE can be allowedaccording to an operator's policy or the like.

More specifically, the PCRF 58 a may verify whether the IMS registrationis requested from the normal UE 10 by verifying whether an initialaccess procedure for an EPS network of the UE 10 is performed accordingto a normal procedure, whether a PDN connectivity is normally generated,whether a register message for the IMS registration is transmittedthrough the normally generated PDN connectivity, or whether itcorresponds to the normal UE on the basis of subscriber informationobtained from a user data repository (UDR) or a user subscriptionrepository (SPR). In addition, the PCRF 58 a may verify whether the IMSregistration is requested from the normal UE 10 in comparison with anidentifier and IP address (i.e., information acquired in an EPS level)of a UE which has established a PDN connectivity and an identifier andIP address (i.e., information acquired in an IMS level) of the UE 10which has transmitted the register message. That is, the PCRF 58 a mayverify whether the IMS registration is requested from the malicious UE10.

In addition, even if the IMS registration is requested from the normalUE 10, the PCRF 58 a may verify whether it is allowed to provide aPLMN-ID to the P-CSCF 61 a in accordance with a roaming agreement of anoperator or a local policy of the operator.

If the IMS registration is requested from the malicious UE 10 or if itis not allowed to provide the PLMN-ID to the P-CSCF 61 a according tothe operator's policy, the PCRF 58 a may transmit a negative responsefor a notification subscription request for the PLMN change of theP-CSCF 61 a (S607).

When the negative response is received from the PCRF 58 a, the P-CSCF 61transmits an IMS registration failure message to the UE 10 (S609).

4. Fourth Scheme According to a Disclosure of the Present Specification

The fourth scheme according to the disclosure of the presentspecification is a scheme for releasing a pre-generated Rx interfacewhen an IMS registration of the UE 10 fails in an IMS registrationprocedure.

FIG. 14 is signal flow diagram showing a fourth scheme according to adisclosure of the present specification.

A case where a message for informing an IMS registration failure to theP-CSCF 61 a is received after a PLMN-ID change notification issubscribed to the PCRF 58 a through a pre-generated Rx interface isassumed in the scheme according to FIG. 14. A notification registrationprocedure for a PLMN-ID change and an Rx interface generation of theP-CSCF 61 a is the same as described above with reference to FIG. 11 toFIG. 13.

Referring to FIG. 14, the P-CSCF 61 a, which has received a message fornotifying the IMS registration failure, requests the PCRF 58 a torelease the PLMN-ID change notification (S701).

The PCRF 58 a configures the P-GW 53 a not to report the PLMN-ID changeany more (S703). In addition, the P-CSCF 61 a releases an Rx interfacegenerated between the P-CSCF 61 and the PCRF 58 a.

FIG. 15 is a flowchart showing a method in which the P-CSCF performs thefirst scheme according to a disclosure of the present specification.

Referring to FIG. 15, the P-CSCF receives a register message from the UE(S801). The P-CSCF holds a delivery of the received register message,and generates a temporary register message (S803).

The P-CSCF transmits the generated temporary register message to theI-CSCF (S805). The P-CSCF receives a response message from the I-CSCF(S807).

The P-CSCF verifies whether the received response message is a 401unauthorized message (S809). As a result of the verification, if it is a401 unauthorized message, the P-CSCF discards the response message andgenerates an Rx interface for transmitting and receiving data withrespect to the PCRF (S811). On the contrary, if the registration to theIMS network is not allowed, the P-CSCF transmits an IMS registrationfailure message to the UE and ends this process (S813).

The P-CSCF subscribes a PLMN-ID change notification to the PCRF throughthe Rx interface (S815). The P-CSCF receives a report for the PLMN-IDfrom the PCRF (S817). The P-CSCF adds the PLMN-ID to a header of theheld register message and transmits it to the I-CSCF (S819).

FIG. 16 is a flowchart showing a method in which the P-CSCF performs thesecond scheme according to a disclosure of the present specification.

Referring to FIG. 16, the P-CSCF transmits a register message receivedfrom the UE to the I-CSCF (S901). The P-CSCF receives a response messagefrom the l-CSCF (S903).

The P-CSCF verifies whether the received response message is a messagefor allowing a registration to the IMS network of the UE (S905). Herein,the message for allowing the registration to the IMS network may beeither a 401 unauthorized message or a 200 OK message.

As a result of the verification, if the message allows the registrationto the IMS network, the P-CSCF transmits a response message to the UE(S907). In addition, the P-CSCF generates an RX interface fortransmitting and receiving data with respect to the PCRF (S909). On thecontrary, if the registration to the IMS network is not allowed, theP-CSCF transmits an IMS registration failure message to the UE (S911).

The P-CSCF subscribes a PLMN-ID change notification to the PCRF throughthe Rx interface (S913). The P-CSCF receives a report for the PLMN-IDfrom the PCRF (S915).

The P-CSCF receives a new register message from the UE (S917). TheP-CSCF adds the PLMN-ID to a header of a new register message andtransmits it to the I-CSCF (S919).

The aforementioned embodiments of the present invention can beimplemented through various means. For example, the embodiments of thepresent invention can be implemented in hardware, firmware, software,combination of them, etc.

FIG. 17 is a block diagram showing a structure of a UE and a P-CSCFaccording to a disclosure of the present specification.

The UE 100 includes a processor 101, a memory 102, and an RF unit 103.The memory 102 is connected to the processor 101 to store variousinformation for driving the processor 101. The RF unit 103 is connectedto the processor 101 to transmit and/receive a wireless signal. Theprocessor 101 implements a suggested function, procedure, and/or method.

The P-CSCF 200 includes a processor 201, a memory 202, and a radiofrequency RF unit 203. The memory 202 is connected to the processor 201to store various information for driving the processor 201. The RF unit203 is connected to the processor 201 to transmit and/receive a wirelesssignal. The processor 201 implements a suggested function, procedure,and/or method. An operation of the base station 200 according to theabove embodiment may be implemented by the processor 201.

The processor may include an application-specific integrated circuit(ASIC), another chipset, a logic circuit, and/or a data processor. Amemory may include read-only memory (ROM), random access memory (RAM), aflash memory, a memory card, a storage medium, and/or other storagedevices. An RF unit may include a baseband circuit to process an RFsignal. When the embodiment is implemented, the above scheme may beimplemented by a module procedure, function, and the like to perform theabove function. The module is stored in the memory and may beimplemented by the processor. The memory may be located inside oroutside the processor, and may be connected to the processor throughvarious known means.

In the above exemplary system, although methods are described based on aflowchart including a series of steps or blocks, the present inventionis limited to an order of the steps. Some steps may be generated in theorder different from or simultaneously with the above other steps.Further, it is well known to those skilled in the art that the stepsincluded in the flowchart are not exclusive but include other steps orone or more steps in the flowchart may be eliminated without exerting aninfluence on a scope of the present invention.

What is claimed is:
 1. A method for obtaining an identifier of a visitedpublic land mobile network (V-PLMN) in order to register a userequipment (UE), which has roamed to the V-PLMN, to an IP multimediasubsystem (IMS) network, the method performed by a proxy-call sessioncontrol function (P-CSCF) and comprising: when a request message toregister to the IMS network is received from the UE, transmitting, bythe P-CSCF, the request message to an interrogating-CSCF (I-CSCF);receiving, by the P-CSCF, a response message from the I-CSCF in responseto the transmission of the request message; when the received responsemessage is a 401 unauthorized message, transmitting, by the P-CSCF, theresponse message to the UE; when the received response message is the401 unauthorized message, generating, by the P-CSCF, a reception (Rx)interface for transmitting and receiving data with respect to a policyand charging rule function (PCRF); receiving, by the P-CSCF, theidentifier of the V-PLMN from the PCRF through the Rx interface; andtransmitting, by the P-CSCF, the identifier of the V-PLMN to the I-CSCF.2. The method of claim 1, further comprising: if a new request messageto register to the IMS network is received from the UE, transmitting, bythe P-CSCF, the new request message to the I-CSCF by adding theidentifier of the V-PLMN to a header of the new request message.
 3. Themethod of claim 1, wherein in the receiving of the identifier of theV-PLMN, a notification for a change in the identifier of the V-PLMN issubscribed for the PCRF through the Rx interface, and the identifier ofthe V-PLMN is received from the PCRF.
 4. A method for obtaining anidentifier of a visited public land mobile network (V-PLMN) in order toregister a user equipment (UE), which has roamed to the V-PLMN, to an IPmultimedia subsystem (IMS) network, the method performed by a proxy-callsession control function (P-CSCF) and comprising: when a request messageto register to the IMS network is received from the UE, holding, by theP-CSCF, the request message and generating a temporary register message;transmitting, by the P-CSCF, the generated temporary register message toan interrogating-CSCF (I-CSCF), and receiving a response message; whenthe received response message is a message for allowing the registrationto the IMS network, discarding, by the P-CSCF, the response message, andgenerating an interface for transmitting/receiving data with respect toan entity of an Evolved Packet Core (EPC) network; and receiving, by theP-CSCF, the identifier of the V-PLMN from the entity of the EPC throughthe interface.
 5. The method of claim 4, further comprising:transmitting, by the P-CSCF, the request message to the I-CSCF by addingthe identifier of the V-PLMN to a header of the held request message. 6.The method of claim 4, wherein in the receiving of the identifier of theV-PLMN, a notification for a change in the identifier of the V-PLMN issubscribed for the entity of the EPC network through the interface, andthe identifier of the V-PLMN is received from the entity of the EPCnetwork.
 7. The method of claim 4, wherein if the entity of the EPCnetwork is a policy and charging rule function (PCRF), the interface isa reception (Rx) interface.
 8. The method of claim 4, wherein themessage for allowing the registration to the IMS network is any one of a401 unauthorized message and a 200 OK message.
 9. A proxy-call sessioncontrol function (P-CSCF) for obtaining an identifier of a visitedpublic land mobile network (V-PLMN) in order to register a userequipment (UE), which has roamed to the V-PLMN, to an IP multimediasubsystem (IMS) network, the P-CSCF comprising: a transceiver; and aprocessor controlling the transceiver, wherein the processor isconfigured to: when a request message to register to the IMS network isreceived from the UE, control the transceiver to transmit the requestmessage to an interrogating-CSCF (I-CSCF); control the transceiver toreceive a response message from the I-CSCF in response to thetransmission of the request message; control the transceiver to transmitthe response message to the UE, when the received response message is a401 unauthorized message; generate a reception (Rx) interface fortransmitting and receiving data with respect to a policy and chargingrule function (PCRF), when the received response message is the 401unauthorized message; control the transceiver to receive the identifierof the V-PLMN from the PCRF through the Rx interface; and control thetransceiver to transmit the identifier of the V-PLMN to the I-CSCF. 10.The P-CSCF of claim 9, wherein if a new request message to register tothe IMS network is received from the UE, the processor transmits the newrequest message to the I-CSCF by adding the identifier of the V-PLMN toa header of the new request message.
 11. A proxy-call session controlfunction (P-CSCF) for obtaining an identifier of a visited public landmobile network (V-PLMN) in order to register a user equipment (UE),which has roamed to the V-PLMN, to an IP multimedia subsystem (IMS)network, the P-CSCF comprising: a transceiver; and a processorcontrolling the transceiver, wherein the processor is configured to:when a request message to register to the IMS network is received fromthe UE, hold the request message and generate a temporary registermessage; control the transceiver to transmit the generated temporaryregister message to an interrogating-CSCF (I-CSCF), and receive aresponse message; control the transceiver to discard the responsemessage, and generate an interface for transmitting/receiving data withrespect to an entity of an Evolved Packet Core (EPC) network, when thereceived response message is a message for allowing the registration tothe IMS network; and control the transceiver to receive the identifierof the V-PLMN from the entity of the EPC through the interface.
 12. TheP-CSCF of claim 11, wherein the processor transmits the request messageto the I-CSCF by adding the identifier of the V-PLMN to a header of theheld request message.
 13. The P-CSCF of claim 11, wherein the messagefor allowing the registration to the IMS network is any one of a 401unauthorized message and a 200 OK message.